Burner for a heater  with improved fuel supply, improved heat shield and improved baffle plate

ABSTRACT

A burner for a heater, especially for motor vehicles, has an essentially axially symmetrical combustion chamber, a burner nozzle for supply and atomization of fuel, a fuel needle for supplying fuel to the combustion chamber, a combustion air supply for supplying combustion air to the combustion chamber, a starting zone in which ignition of the fuel to start the burner takes place, a heat shield between the burner nozzle and the combustion chamber, the heat shield having openings for supplying secondary air to the combustion chamber, and a baffle plate located in the combustion chamber. By choosing the inside diameter of the fuel needle, the exit speed of the fuel is predetermined such that, during the starting phase of the burner; fuel in essentially unatomized form reaches the starting zone. The openings have air guide elements, and the baffle plate has a defined curvature in the axial direction.

BACKGROUND OF THE INVENTION

1. Field of Invention

The invention relates to a burner for a heater, especially for use inmotor vehicles, with an essentially axially symmetrical combustionchamber, a burner nozzle for supply and atomization of fuel, which has afuel needle for supplying fuel to the combustion chamber and acombustion air supply for supplying combustion air to the combustionchamber, a starting zone in which ignition of the fuel to start theburner takes place, a heat shield between the burner nozzle and thecombustion chamber, the heat shield having openings for supplyingsecondary air to the combustion chamber, and a baffle plate which islocated in the combustion chamber.

2. Description of Related Art

Burners of the initially described type, which are also calledatomization burners or spray burners, are used especially in auxiliaryheaters and independent heaters for motor vehicles.

There are numerous requirements for these burners, especially withrespect to reliable and largely emission-free starting behavior andstable combustion operation. Furthermore, an effort is made to buildheaters which can be used in different installation positions.

With respect to starting behavior, various operating parameters must bematched to one another. On the one hand, it is necessary during burnerstart to make available a relatively rich fuel-air mixture in thestarting zone, and on the other hand, providing a sufficient amount ofprimary combustion air is necessary to ensure transport of fuel from thefuel needle to the starting zone.

The requirement of allowing different installation positions of theheater is associated with problems relating to starting behavior.Specifically, to be able to transport fuel into the starting zone withlow primary air supply, in the past, orienting the fuel needle with theoutlet opening pointed down had to be tolerated; this resulted in theentire burner having to be mounted in a vertical installation position.

To ensure stable combustion operation of the burner, likewise, mutuallycontradictory requirements must be satisfied. On the one hand, goodintermixing of the fuel and air is always required, and on the otherhand, especially during the starting phase, it is undesirable to causeoverly high air proportions and overly high swirling in the core regionof the flame.

Commonly-owned, U.S. patent application Ser. No. 10/466,683 discloses areformer with a reaction space in which a breaker body is located thatcan be made conical and/or convex and/or concave at least in sections.The breaker body comprises a baffle plate in which openings can be madein the form of defined perforations. The baffle plate can have a chamberinto which at least one heating element extends and can be used as astarting chamber, in which case the heating element is formed by a glowpin and/or a glow plug that can be activated to initiate burneroperation of the reformer system. Additionally, an air guidance meanscan be provided in the air inlet area to impart a swirl to thein-flowing air. The air guidance means can comprise an air-guidingdevice with swirl blades that are located on a carrier mounted on aVenturi nozzle assembly, and the blades can have triangular basesurfaces with rounded corners.

SUMMARY OF THE INVENTION

The object of the invention is to overcome the described problems of theprior art at least in part and especially to enable reliable andlow-emission starting behavior with little dense smoke in differentinstallation positions.

This object is achieved by choosing the inside diameter of the fuel sothat the exit speed of the fuel is predetermined such that, during thestarting phase of the burner, fuel in essentially unatomized formreaches the starting zone, by the heat shield having openings that areequipped with air guide elements, and by the baffle plate having adefined curvature in the axial direction.

The invention is based on a generic burner in that by choosing theinside diameter of the fuel needle, the exit speed of the fuel ispredetermined such that during the starting phase of the burner fuelreaches the starting zone in essentially unatomized form, that theopenings in the heat shield are equipped with air guide elements, andthat the baffle plate has a defined curvature in the axial direction. Byreducing the inside diameter of the fuel needle as compared to fuelneedles in the heaters of the prior art, at the same fuel deliveryvolume, the exit speed of the fuel is increased. In this way, for anyinstallation position, it is possible for the fuel jet to reach thestarting zone from the exit opening of the fuel needle. In particular,for a small primary air amount, for which the supplied primary airshould have only little angular momentum, an essentially unatomized fueljet can reach the starting zone. Consequently, the burner startsreliably and formation of dense smoke during starting is distinctlyreduced. A heat shield is fundamentally useful to shield the nozzle andthe fuel supply against the heat energy present in the combustionchamber. Furthermore, secondary air is supplied to the combustion spacevia the heat shield. By the openings for secondary air supply beingprovided with air guide elements, this secondary air can be supplied ina controlled manner so that combustion operation, both with respect tostarting operation and also for continuous operation, can be influencedin a specific manner. For the baffle plates of the prior art which aremade flat, this is among others not the case since depending on thetemperature spontaneous changes of shape can occur which can adverselyaffect the combustion behavior of the burner.

It is preferred that the inside diameter of the fuel needle be between0.5 mm and 0.7 mm. As compared to exit speeds for fuel needles of theprior art in which the inside diameter is in the region of 0.8 mm, theexit speed for inside diameters between 0.5 mm and 0.7 mm can be almostdoubled or even more than doubled.

It is especially preferred that the inside diameter of the fuel needleis roughly 0.6 mm. At this inside diameter, in full load operation,i.e., at a fuel mass flow of 0.5 kg/h, exit speeds of more than 0.6 m/sare possible, while for an inside diameter of 0.8 mm the exit speed isin the region of 0.35 m/s. The exit speed in partial load operationrises accordingly, i.e., for a fuel mass flow of 0.2 kg/h, from roughly0.14 m/s to roughly 0.25 m/s. For a corresponding choice of constructionproperties or of operating parameters, the goal of an essentiallyunatomized jet which reaches the starting zone when the heater is beingstarted can be achieved even with a conventional fuel needle with aninside diameter of roughly 0.8 mm.

It is useful for the starting zone to be made as a starting chamber intowhich an ignition element projects. The wall of the combustion chambercan surround the ignition element in this way. During startingoperation, the “ballistic” fuel jet can then wet the ignition elementand the combustion chamber wall with fuel so that the combustion chamberwall and adjacent components after their heating are used as wallvaporizers.

It is useful for the air guide elements to be formed by tabs which aremade integrally with the heat shield and which project in the directionof the combustion chamber. This heat shield can be easily produced, forexample, by the tabs being formed with a V-shaped punching tool andbeing bent out of the plane of the heat shield after or with thepunching process.

The invention is also usefully developed in that the tabs are made atdifferent angles relative to the surface of the heat shield and/or tothe radius of the heat shield. If the tabs extend almost perpendicularlyto the radius of the heat shield, this delivers strong angular momentum,while tabs with a smaller angle to the radius deliver smaller angularmomentum. Tabs which assume a small angle to the surface of the heatshield produce air flows which have a large radial component and a smallaxial component, while for tabs with large angles to the surface of theheat shield the axial component dominates. In this way, it is possibleto route secondary air with low angular momentum into the core region offlame formation. Thus, the air required for combustion is supplied; butthere is no excess angular momentum which would adversely affectstabilization of the flame. In particular, the secondary air can bedivided depending on the alignment of the individual air guide elements.

According to another embodiment, it is provided that the tabs aregrouped at essentially identical angles to the surface of the heatshield and/or to the radius of the heat shield. Defined flow states inthe combustion chamber are formed by the collective alignment of thetabs.

The invention is also usefully executed such that the burner has aburnout zone and that the secondary air which is supplied to the burnoutzone has higher angular momentum than the secondary air which issupplied to the starting zone. High angular momentum is desired in theburnout zone. In particular a radially inside swirled backflow regionimproves the burnout and provides for the combustion chamber volumebeing effectively used.

It is preferred that there is a curvature in the direction of theburnout zone. In this way, a sufficient space in the region of thestarting chamber is made available. Furthermore, it has been found thatthe curvature in the direction of the burnout zone does not have anadverse effect on the flow behavior in this zone. In particular, thepronounced swirled backflow region is maintained in the radially insideregion of the burnout zone.

According to one preferred embodiment of the invention, it is providedthat the outer periphery of the baffle plate defines a plane and thatthe ratio between the maximum axial distance of the baffle plate fromthis plane and the diameter of the baffle plate is between 0.07 and0.21. The most heavily arched point of the baffle plate is preferablyessentially in the center of the arrangement with respect to the radialcoordinate. From the plane which is defined by the outer periphery ofthe baffle plate, this point has an axial distance which is defined bythe indicated ratio to the diameter.

In this connection, it is especially preferred that a ratio of about0.14 is produced between the maximum axial distance of the baffle platefrom the plane and the diameter of the baffle plate. For example, theround diameter of baffle plate is roughly 40 mm, while the curvature hasa value of roughly 5.7 mm.

The invention is based on the finding that the novel fuel supply with afuel needle with a reduced exit cross section, the novel heat shieldwith air guide elements and the novel, curved baffle plate can greatlyimprove the operating behavior of a burner. This relates especially tothe starting behavior, the stability of burner operation andpossibilities with respect to the installation position of the burner inthe motor vehicle.

The invention is explained by way of example with reference to theaccompanying drawings using preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of the burner in accordance with theinvention;

FIG. 2 is a perspective of a burner flange with the heat shield insertedtherein; and

FIG. 3 shows a perspective of the heat shield.

DETAILED DESCRIPTION OF THE INVENTION

In the following description of preferred embodiments of the invention,the same reference numbers label the same or comparable components.

FIG. 1 shows a sectional view of a burner 10 of the invention. Theburner 10 has a nozzle 12 which is securely joined to the heat shield24. The heat shield 24, together with a burner pipe 40 which isconnected to the heat shield 24, defines a combustion chamber 22. Thecombustion chamber pipe 40 is surrounded by an outer pipe 42 which formsthe burner flange. A flame tube 38 is attached to this outer pipe 42.The connections between the heat shield 24 and the combustion chamberpipe 40 or between the combustion chamber pipe 40, the outer pipe 42 andthe flame tube 38 are generally welded connections. On the fuel nozzle12, there is a fuel supply 50 which has a metal pipe 52 for supply offuel and a fuel needle 14 for injection of fuel into the combustionchamber 22. Furthermore, in the region of the fuel nozzle 16, there arechannels for supplying primary combustion air into the fuel nozzle 20.The primary combustion air flows past the fuel needle 14 in order tothen flow along the radially widening air guide of the fuel nozzle 12 inthe direction of the combustion chamber, and finally, into thecombustion chamber 22. The radial widening of the air guide achievesimproved atomization due to the Venturi effect. Within the combustionchamber 22, there is also a baffle plate 36 which has an advantageouscurvature. This curvature in the direction of the burnout zone 32 isadvantageous since, in this way, heat-induced spontaneous changes in theshape of the baffle plate 36 are prevented. Moreover, by curving thebaffle plate 36 in the direction of the burnout zone 32, sufficientspace is available for accommodating the starting chamber 18. The wallwhich defines the starting chamber 18 is welded to the baffle plate 36.

FIG. 2 is a perspective view of the burner flange with the heat shield24 inserted into it, and FIG. 3 shows a perspective view of heat shield24. Furthermore, reference is likewise made below to burner componentsas shown in FIG. 1. The heat shield 24 has a central opening 48 throughwhich the fuel-air mixture which has been delivered from the nozzle 12enters the combustion chamber. Also, there is a laterally arrangedopening 34 through which the ignition element 20 is routed. On the heatshield 24, there are attachment pins 44, 46 to which the nozzle 12 isattached. Additionally, the heat shield 24 has a host of openings 26through which secondary air can enter the combustion chamber 22. On theside of the heat shield 24 facing the combustion chamber 22, there aretriangular air guide elements 28, 30. They cause division of thesecondary air based on their different angles relative to the radius ofthe heat shield 24. A first group of air guide elements with memberspartially labeled with reference number 28 are aligned at a large anglerelative to the radius of the heat shield 24, i.e., their alignment isessentially or almost tangential. Based on this alignment, the secondaryair passing through the corresponding openings 26, with an exit flowdirection indicated by the arrow, will overflow into the burnout zone 32past the baffle plate 36 with high angular momentum.

This air which is provided with a high angular momentum flows in theradially outlying region of the burnout zone 32 into the posteriorregion of the combustion chamber 32, i.e., into the region of thecombustion chamber 22 which faces away from the heat shield 24, andthen, with high swirling in the central region, back in the direction ofthe baffle plate 36. Consequently, advantageous mixing of the gaseouscomponents in the burnout zone 32 occurs. Another group of air guideelements 30 is arranged at a smaller angle relative to the radius of theheat shield 24. These air guide elements are partially identified withthe reference number 30. Moreover, these air guide elements 30 have asmaller angle relative to the surface of the heat shield 24 than the airguide elements 28. Consequently, these air guide elements 30 route thesecondary air with an exit flow direction (indicated by another arrow)with low angular momentum into the core region of the flame; thisespecially benefits stable combustion chamber behavior.

Thus, a novel spray burner is made available which is improved withrespect to the possible installation positions, the starting behaviorand the behavior in continuous operation. Furthermore, problems withrespect to temperature-induced changes of the shape of the baffle plateare avoided.

The features of the invention disclosed in the above specification, thedrawings and the claims can be important to the implementation of theinvention both individually and also in any combination.

1. Burner for a heater, especially for use in motor vehicles, with anessentially axially symmetrical combustion chamber (22), a burner nozzle(12) for supply and atomization of fuel, which has a fuel needle (14)for supplying fuel to the combustion chamber (22) and a combustion airsupply (16) for supplying combustion air to the combustion chamber, astarting zone (18) in which ignition of the fuel to start the burnertakes place, a heat shield between the burner nozzle and the combustionchamber, the heat shield having openings for supplying secondary air tothe combustion chamber, and a baffle plate which is located in thecombustion chamber, wherein the inside diameter of the fuel needle (14)is sized to produce a predetermined exit speed of the fuel such that,during the starting phase of the burner (10), fuel in essentiallyunatomized form reaches the starting zone (18), the openings areequipped with air guide elements, and the baffle plate has a definedcurvature in an axial direction.
 2. Burner as claimed in claim 1,wherein the inside diameter of the fuel needle (14) is between 0.5 and0.7 mm.
 3. Burner as claimed in claim 1, wherein the inside diameter ofthe fuel needle (12) is roughly 0.6 mm.
 4. Burner as claimed in claim 1,wherein the starting zone is made as a starting chamber (18) into whichan ignition element (20) projects.
 5. Burner as claimed in claim 1,wherein the air guide elements are formed by tabs (28, 30) which aremade integrally with the heat shield and which project toward thecombustion chamber.
 6. Burner as claimed in claim 5, wherein the tabs(28, 30) are made at different angles relative to at least one of thesurface of the heat shield and the radius of the heat shield (24). 7.Burner as claimed in claim 5, wherein the tabs (28, 30) are grouped atessentially identical angles relative to at least one of the surface ofthe heat shield and the radius of the heat shield.
 8. Burner as claimedin claim 1, wherein the combustion chamber of the burner (10) has aburnout zone (32) and wherein the secondary air is supplied to theburnout zone with a higher angular momentum than secondary air issupplied to the starting zone.
 9. Burner as claimed in claim 1, whereinthe heat shield (24) has an opening (34) for routing the ignitionelement through.
 10. Burner as claimed in claim 1, wherein the curvatureof the baffle plate (36) extends toward the burnout zone (30). 11.Burner as claimed in claim 1, wherein an outer periphery of the baffleplate defines a plane and wherein a ratio between a maximum axialdistance of the baffle plate from said plane and the diameter of thebaffle plate is between 0.07 and 0.21.
 12. Burner as claimed in claim11, wherein the ratio between the maximum axial distance of the baffleplate (36) from the plane and the diameter of the baffle plate (36) isroughly 0.14.